f2fs: support superblock checksum

Now we support crc32 checksum for superblock.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Junling Zheng <zhengjunling@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 218695e..a449132 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2178,6 +2178,26 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
 					(bh->b_data + F2FS_SUPER_OFFSET);
 	struct super_block *sb = sbi->sb;
 	unsigned int blocksize;
+	size_t crc_offset = 0;
+	__u32 crc = 0;
+
+	/* Check checksum_offset and crc in superblock */
+	if (le32_to_cpu(raw_super->feature) & F2FS_FEATURE_SB_CHKSUM) {
+		crc_offset = le32_to_cpu(raw_super->checksum_offset);
+		if (crc_offset !=
+			offsetof(struct f2fs_super_block, crc)) {
+			f2fs_msg(sb, KERN_INFO,
+				"Invalid SB checksum offset: %zu",
+				crc_offset);
+			return 1;
+		}
+		crc = le32_to_cpu(raw_super->crc);
+		if (!f2fs_crc_valid(sbi, crc, raw_super, crc_offset)) {
+			f2fs_msg(sb, KERN_INFO,
+				"Invalid SB checksum value: %u", crc);
+			return 1;
+		}
+	}
 
 	if (F2FS_SUPER_MAGIC != le32_to_cpu(raw_super->magic)) {
 		f2fs_msg(sb, KERN_INFO,
@@ -2635,6 +2655,7 @@ static int read_raw_super_block(struct f2fs_sb_info *sbi,
 int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
 {
 	struct buffer_head *bh;
+	__u32 crc = 0;
 	int err;
 
 	if ((recover && f2fs_readonly(sbi->sb)) ||
@@ -2643,6 +2664,13 @@ int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
 		return -EROFS;
 	}
 
+	/* we should update superblock crc here */
+	if (!recover && f2fs_sb_has_sb_chksum(sbi->sb)) {
+		crc = f2fs_crc32(sbi, F2FS_RAW_SUPER(sbi),
+				offsetof(struct f2fs_super_block, crc));
+		F2FS_RAW_SUPER(sbi)->crc = cpu_to_le32(crc);
+	}
+
 	/* write back-up superblock first */
 	bh = sb_bread(sbi->sb, sbi->valid_super_block ? 0 : 1);
 	if (!bh)